1. Field of the Invention
The present invention relates to a circuit board in which a viahole is easily formed and a method of manufacturing the same.
2. Description of the Related Art
In general, an electronic product includes many elements, and small electronic elements are mounted on a circuit board in the electronic product. The circuit board includes a substrate and a circuit pattern. The substrate includes an insulating material and a conductive layer. The circuit pattern is formed on the conductive layer.
Specifically, a circuit board includes a copper film that forms a circuit pattern electrically connecting chips, resistors, and capacitors, and a substrate formed of a resin material. The circuit board has a plurality of viaholes to connect the circuit pattern to electronic elements, or to connect circuit patterns disposed on different layers to each other.
Viaholes are formed in the circuit board with a laser drill. Since laser energy is absorbed poorly by the copper film formed on the substrate, the efficiency of the process of forming viaholes with the laser drill is low. Low process efficiency leads to longer process time, lower yield, and more variation in the size and shape of the viaholes.
Furthermore, due to such poor absorption of laser, smears, such as ash or tarr, are generated when copper, resin, or glass in the substrate evaporate, and the generated smears are attached around the viaholes.
To increase laser absorption and viahole formation process efficiency, the surface of the circuit board can be black oxidized or coated with a material that has a high laser absorption rate.
Specifically, the circuit substrate can be surface-treated by black oxidation or coated with black or brown oxide. However, such conventional surface treatment processes require a wetting process and thus, additional efforts at managing and operating the overall manufacturing process. In addition, there are physical limitations to the improvement of laser absorption.